Cermark MLD-28cc Gas Engine Review

Join Dr. Dave as he burns some fuel, turns some props and makes some noise reviewing this extensive line-up of gas/oil two-stroke motors.

Introduction to Testing

I was fortunate to have access to four different engines all at the same time for testing and comparison. To say the least it was a task of some duration, but one that gave me special insight and understanding of not only gas engines both propeller selection.

Method

My approach for all the engines was to first break them in using a 24:1 mix of gas and oil: rich with oil (Polaris Premium Synthetic Blend), but plenty of lubricant for the break-in. I ran 87 octane (blended with ethanol) as that is what is available in this area. Each engine had one gallon of fuel run through it with the designated break-in prop. For the first three quarters of the gallon the engines were run no more than 10 minutes and then allowed to fully cool. During each 10-minute cycle the throttle was manipulated to make sure a variable RPM was achieved. Cylinder head temps were taken with an infrared temp sensor during the runs to make sure nothing was overheating. All starts were by hand.

Towards the end of the each gallon I would advance the throttle from stop to stop periodically. With the exception of the SPE-43cc engine I never touched the needle valves, but it was just too rich in the 100 degree air and 60% humidity to run well so I leaned that engine back very slightly to improve the run. All the engines were run with a 6 volt NiMH battery with a capacity of 1200 or greater mAh: the 3mm 50cc TOC was run with a 4.8 volt battery.

My tank was about 18 ounces and three runs consumed the full tank for all the engines typically. The throttle was varied within each ten minute run multiple times. Starting was easy, and once I established a routine for choking, the process became very predictable. I found it necessary to choke all the engines before each start. I also found they started better if I cracked open the throttle just a bit to allow some air. After starting, I moved immediately to idle to allow for warm up.

I set the props to load compression at about 12:00 and to break-over at about 10:00 to 11:00. It is easier and safer if your flip is away from the engine and down. Periodically I would re-torque the prop to the hub. Early runs typically were full of vibration that settled out after a gallon or so and after I backed off the oil and adjusted the carburetor.

Master Airscrew Propellers

All the props for this project were provided by Master Airscrew . Started in 1977 by Fred Jamieson, the Master Airscrew brand is well known among flyers worldwide. The fine people from Master Airscrew provided me some information I want to share with you regarding their line of propellers.

In their shop they produce all their injection molded props starting first from CAD designs. Props between 6" and 20" are produced and then tested for strength continuously throughout the production process and checked for balance, warping and appearance. The nine professionals working at Master Airscrew ensure, through their combined total of almost 100 years of service, that each and every prop leaving the shop is perfect, and I can confirm that claim. Their wooden props are imported from Italy.

Over the last thirty years they have been innovators by paying close attention to the needs of modelers. They offer a high quality prop at a good price and great customer service. Be on the lookout for their new line of Formula One Series propellers: they are sure to be a wonderful addition to an already excellent lineup.

About the Props

All props required their center hole to be drilled out and at least two smaller prop bolts to be drilled. I used a drill press and set up a jig so I could make sure I centered the hub bolt. The prop washer helped me align the two secondary bolts. The props were then checked for balance.

Balancing of the composite props typically was not a problem; My method was to sand off or scrape off the heavier end until I felt comfortable that no more should be removed. If needed, I sprayed clear acrylic paint to the light tip in layers to add weight. The Master Airscrew line of props was exceptional throughout the testing process.

All props bolts had torque applied using PB Swiss’s torque drivers, ensuring uniform compression of the prop hub. Wooden props require re-tightening after each run until the prop settles into the hub. Torque settings were approximately 3.0 ft lbs / 36 in lbs.

Test stand

I constructed a test stand using lite-ply and fiber-glassed the front, sides and all corners. This is important to make sure the stand does not rattle, vibrate or come apart. The fiberglass also keeps the fuel from softening the lite-ply. Surprisingly, you get very little fuel on the firewall with gassers. I mounted the stand to a large picnic table so that there was no chance of any movement.

Thrust

The test stand was hinged so it could tilt forward. The stand was tall so a cable was connected to the stand and the picnic table with a fish scale in the middle. A second cable was attached to the stand to make sure nothing could move forward beyond the movement of the scale which proved very effective.

Comparing Engines During Break-in

I want to be clear that I am not making any comparisons of the engines through their break-in. The rich mixture and higher oil content just do not make the comparisons worth much. The break-in process is a necessity though.

I began the break-in of the four engines with the SPE-26 and followed with the MLD-28. Both engines share the same firewall bolt pattern and the SPE 26, SPE 43 and MLD-28 share the same three-bolt prop hub pattern.

Spark Plugs

I used the original equipment and then replaced it when the prop testing was done. I found no problems with any of the plugs.

Engine Prototypes

The MLD-28 and SPE-43 engines were early prototypes. At press time the MLD-28 is being sold with a different CDI ignition and velocity stack as the MLD-28S. The SPE-46 was upgraded from the SPE-40. The SPE-43 is being shipped with a different timing setup and some slight internal modifications from the engine I tested.

The MLD–28 engine differs only slightly from the SPE–26: It has a flat cylinder head, the spark plug is centered over the piston, and the cylinder head is slightly larger on the outside. But they look and weigh the same with no difference in the prop hub or carburetor. There is a slight increase in the brake horsepower using the same carburetor and ignition module. The MLD-28 uses two bearings to support the crankshaft and a three bolt prop hub.

Downloads

Startup and Break-in

I had the same success with the first start on the MLD-28 that I had with the SPE-26: After about 10-15 flips it started. The MLD-28 surged a lot around 4,000 RPM through the first few tanks, but I never touched the needle valve. The surging was due to the high oil mix and rich fuel mix that was necessary for the break-in. The engine operated initially between 3,500 RPM and 7,500 RPM but had much higher head temps ranging closer to 240 degrees as the throttle increased. Crankcase temperatures were around 110 degrees.

The MLD-28 used the same 16 x 8 prop for break-in with the same bolt pattern as the SPE 26. After few tanks, the MLD-28 smoothed out.

MLD 28 Prop Tests

Before starting the test I changed the spark plug and noted nothing out of the ordinary on the break-in plug. The MLD-28 ran great on the 40:1 mix and actually ran slightly cooler. Startup was always quick, and the idle was really strong even at very low RPM. I could get the idle down in the 1500 range, and it would purr all day but quickly rev to full RPM instantly. Overall this was one of my favorites of the four I tested.

!!Prop Torque

Wooden props require you to re-torque them after every few runs. You can haphazardly do this by feel, but the correct method is to use a torque gauge. I used PB Swiss’s Torque handle to make sure I got the exact torque on all six bolts. This is especially important since there is no center 10mm bolt to tighten. I applied torque to each bolt in a sequence to 3.02 ft lbs/36.29 in lbs. I tightened the bolts in sequence because head bolts on motors have tightening patterns to spread the load across the head.

Downloads

Test Summary

When I received the MLD-28 it included an older version of the manual. The new version provides some insight into the potential of this engine. As an example, props range from 15 x 8 to 19 x 8 in the new manual while the old version only included four props.

I was very impressed with the MLD-28. From the time is smoothed out in the break-in period I noted my adjustments did not improve on the factory settings. Other than running a little hotter, this engine was a pleasure to work with. I did not have any end play in the crankshaft like I did in the SPE-26. I think the power available in this small package would make it a great engine for anyone wanting to get into gassers.

Conclusion

Properly treated, these Cermark engines are well worth the money and will last a very long time. Product support from Cermark for my testing has been excellent; whatever I needed I was provided and they responded quickly to my needs with a phone call.

I have been looking at this engine to put in my new CMP T-6. I noticed it had just a little more punch than any 26cc I looked at. The price seems right too. Do you know of any in flight dying problems such as the Zenoah G26 has experianced? What about the throttle hookup?

Images

As you look at the carb photos notice how close the choke butterfly is to the outside edge. These photos show the choke closed. I noticed without a velocity stack fuel can be drawn out of the carb because of negative pressure across the opening. So use the velocity stack to reduce this problem.

yes, the MLD-28 comes with velocity stack. However putting it on is optional. All data are taken without velocity stack for standarization.

Peace,
Steven Chao,
Cermark

A velocity stack was not included with the one I bought last month. I have put mine in a 70" SU-31. Assembly is about 90% complete (finishing control linkages and radio installation.) It will be spring before it's in the air. I'll post a flight report then.

Sorry, only the North American version (officially released at the end of October) will have velocity stack, new electronic ignitions, engine registration, and version-3 instruction manual in the engine box. Dave had the unfortunate luck being one of first guinea pig for our MLD-28.

There don't seem to be much action on this thread, but I thought I would give those interested a report on my first flights with the MLD28. I bought the engine and the Edge 540 as a combo deal. I never ran the engine on a test stand but built the plane and then ran the engine for the first time on the plane. Then engine cranked right up using an electric starter. However after the engine was running I experienced terrible interference. The rudder and elevator was going crazy and the throttle servo was also bad. With the help of other club members we began to try to see what the problem was. I relocated everything inside the plane to separate all ignition components as far as possible from all receiver components. This only helped marginally. I tried a different receiver that I had in my WildhareRC Extra and that also helped some. I bypassed switches and done everything imaginable to try to isolate the problem. I finally got it to where only the rudder and elevator was just twitching some. Still not good enough to even think of flying. An older cub member suggested trying some RF filters. I found that JR makes these and I installed a total of 4 of them on the rudder, elevator and throttle leads and one on the switch lead before it goes into the transmitter. To my astonishment that cured the problem. Even though I finally got the RF interference down, I have to conclude that the ignition module must just leak RF noise pretty bad. I have other gassers and never had this much of a problem. I guess I should also mention that I am using a Futaba 9CAP and a PCM receiver.
I put in 5 flights on the Edge, MDL28 combo yesterday and I must say that both plane and engine surpassed my expectations.
I had about one half gallon of fuel ran through the engine with the recommended 32:1 ratio of Penzoil air cooled oil before the first flight. I still had the needles on the rich side but not terribly so. The engine was a little rough in the mid-range but man it makes good power. The plane came out at about 10.3 lbs. and after a got a good feel of the plane I flew in front of the pit area and pulled her up in a hover. It was very solid in a hover. She was hovering a just a bit less that half throttle. Then when I went to full power it didn't rocket out, but did pull out very good straight up and gained more vertical speed the farther she went. I also have the Peakmodels Yak with an OS120AX that I love, but the MLD28 has more power already and it should get alot stronger as it breaks in and I fine tune the engine. Here is the bottom line if you want to fly gas on a 10 pound 3D or aerobatic plane it would be hard to beat this little engine.

We are currently in the process of redesigning the Ignition module. Unfortunately this is the second case of MLD-28 RF noise leakage that we are aware of. Thank you for bring this to our attention. The first one had the sheathing split opened. Was the metal sheathing completely intact?

Sorry to have made you gain some extra weight to the airplane with the 4 iron rings.

Steve, The metal sheathing looked good. I was running an APC 18x6 prop. Sorry I did not get any rpm numbers for you. When you have the redesigned ignition module available I would be interested in getting one from you. My e-mail is bmoody1@peoplepc.com
Let me say to all out there who are considering this engine to not be discouraged by my interference problem. I am sure that this is not a common occurrence and Cermark tried to help me out with the problem even though I bought the engine from Peak Models. I would recommend that you buy the engine from Cermark as I will do if I get another one. One of our club members as already gotten his from Cermark after seeing mine run. The engine is a powerful little beast and is perfect for good 3D power on 25% planes.

We are currently in the process of redesigning the Ignition module. Unfortunately this is the second case of MLD-28 RF noise leakage that we are aware of. Thank you for bring this to our attention. The first one had the sheathing split opened. Was the metal sheathing completely intact?

Sorry to have made you gain some extra weight to the airplane with the 4 iron rings.

What size prop are you using?

Peace,
Steven Chao,
CERMARK

Hi Steven,

First I wanted to thank you for your quick replies to email messages we exchanged a while back. I decided to get the MLD-28. My local Hobby Shop is ordering it for me.

Has the ignition been changed yet? I use a 2.4GHz radio so I know it is less likely to suffer from the problems bluehawkbm reported. I plan to follow the normal setup best practices. Any special cautions I should know about?